This invention relates to techniques for converting crude methanol or other C.sub.1 -C.sub.4 lower aliphatic alcohols to alkyl tertiary-alkyl ethers, di-isopropyl ether (DIPE), and gasoline range hydrocarbons. In particular, this invention relates to an improvement in utilizing methanol-to-gasoline (MTG) processes and operating synfuel systems for converting crude methanol to valuable products by etherifying lower olefins, such as C.sub.3 -C.sub.5 olefins. Methanol is considered the most important oxygenate feedstock because of its widespread availability and low cost. In view of the predominant supply of methanol feedstock, the invention will be discussed primarily with this material as an example: however, it is understood that other lower aliphatic oxygenated hydrocarbons may be employed as the main feedstock or auxiliary streams.
Technical progress of the commercial MTG process has provided an important synthetic fuel source. Also, there has been recent independent development of processes for making alkyl tertiary-alkyl ethers as octane boosters in place of conventional lead additives in gasoline. The etherification processes for the production of methyl tertiary-alkyl ethers, in particular methyl t-butyl ether (MTBE) and t-amyl methyl ether (TAME) have been the focus of considerable research. Recognizing the common feedstock (e.g.--methanol) for the synthetic production of gasoline as well as the production of methyl t-alkyl octane boosting ethers, research workers have endeavored to combine these processes in a manner to provide a synergistically beneficial integrated process. Increasing demand for high octane gasolines blended with lower aliphatic alkyl ethers as octane boosters and supplementary fuels has created a significant demand for isoalkylethers, especially the C.sub.5 to C.sub.7 methyl, ethyl and/or isopropyl t-alkyl ethers, such as methyl t-butyl ether (MTBE). It is known that feedstock dewatering and recovering unreacted methanol by conventional separation and extraction techniques imposes severe economic burdens on the etherification process. Crude methanol usually contains a significant amount of water, typically in the range of 2 to 20 wt %; however, the present invention is useful for removing water in lesser amounts or greater.
It is main object of the present invention to provide a novel and economic technique for removing excess water from crude methanol feedstocks, including novel operating methods and equipment for treating these oxygenate feedstocks prior to etherification and disposing of raffinate containing methanol. It has been discovered that aqueous methanol streams, such as etherification feedstock extraction byproduct can be economically upgraded by catalytic conversion concurrently with hydrocarbons.